i remember when defense secretary leon panetta said that his greatest fear for the united states is a lone wolf attack because it would be impossible to pick up before hand and perhaps then impossible to identify it afterwards. and many have said this could be that kind of situation. are you concerned because there's no suspect? last night they said they had someone they were questioning. that person now is not a perso of interest. what can you tell us about who they're looking at right now and your fears of perhaps never finding the person. >> of course it's a huge concern. usually within the first four hours, that's your best opportunity to apprehend the criminal, in this case the terrorist. i do think the video they have from the scene will help facilitate the appearance of the individual who dropped this backpack into the trash cans. and i think the explosive forensics that's going to be done i think will give us a lot of information to move this information forward. but like you, i am concerned and the lone wolf homegrown terrorist is probably the most difficult to prevent and mo